When using precision rolling bearings, proper bearing installation is crucial to achieve maximum speed and minimize temperature rise.
Bearing installation involves cleaning, drying, and a test run (for grease encapsulation). These procedures should be performed while observing all necessary precautions.
Since sealed bearings contain grease encapsulated inside, they must not be cleaned or dried. Wipe the exterior of the bearings with a clean cloth to remove the rust preventative oil before assembly.
Step 1: Clean the bearings and remove the rust preventative oil.
Soak the bearings in a highly volatile solvent such as refined kerosene or naphthol and clean them by hand. Remove the refined kerosene with gasoline, ethanol, or other solvents. When using an air gun to blow away the cleaning oil, ensure the air is clean. When using oil-air lubrication, bearings can be used directly, but it is recommended to apply or soak them in lubricating oil or a low-viscosity oil after cleaning.
Step 2: Dry the bearings to remove any residual moisture.
When using grease lubrication, the bearings must be thoroughly dried to prevent grease from leaking. Furthermore, grease should be applied immediately after drying. This can be done with warm air (pay attention to air cleanliness) or in a constant temperature bath.
Step 3: Grease Packing.
After packing, manually rotate the rolling element to ensure that the grease is thoroughly applied.
For ball bearings, use a syringe or vinyl bag to apply grease evenly between the balls on the inner ring rolling surface. For ball bearings with a raceway-guided retainer, it is recommended to apply grease to the retainer guide surface using a spatula or other small tool. If the inner ring is too narrow to pack the inner ring rolling surface, pack the outer ring rolling surface. At this point, manually rotate the grease as much as possible to penetrate the inner ring.
When applying grease to the outer diameter (inner diameter) surface of a roller bearing, rotate the roller with your fingertips to ensure that the grease penetrates the inner (outer) ring.
Step 4: Test Run.
1. Oil-air and oil-mist lubrication. With oil lubrication, bearing temperatures stabilize relatively quickly before reaching their peak, making test runs easier. It is recommended to maintain a speed of 2000-3000 rpm for approximately 30 minutes, then gradually increase to the operating speed. However, if the dmn (rolling element center diameter * rotational speed) exceeds 1 million revolutions per minute, for safety reasons, the speed should be increased in increments of 1000-2000 rpm.
2. Grease lubrication. In grease lubrication, a test run is crucial to stabilize the temperature rise. During a test run, the temperature will rise rapidly after the speed increases, and after reaching a peak, the temperature will slowly stabilize. Stabilization requires time.
3. Ball bearings. It is recommended to operate at 1000-2000 rpm, allowing the temperature to stabilize before increasing the speed. If the dmn (rolling element center diameter * rotational speed) exceeds 400,000 revolutions per minute, for safety reasons, the speed should be increased in increments of 500-1000 rpm.
4. Roller bearings. Compared to ball bearings, roller bearings have a longer peak temperature and longer time to reach a stable temperature during a test run. Furthermore, since re-entry of grease may cause a temperature rise and potentially prevent temperature fluctuations from stabilizing, the bearing should be operated at maximum speed for a longer period of time. It is recommended to operate the bearing in increments of 500-1000 rpm, increasing the speed only after the temperature stabilizes. If the dmn (rolling element center diameter * rotational speed) exceeds 300,000 revolutions, the speed should be increased in increments of 300 rpm for safety reasons.
Step 5: Assemble the bearing.
When assembling the bearing on the main shaft, there are two common methods for assembling the bearing: hydraulic press fitting and shrink fitting, where the shaft and the inner ring have an interference fit (tight fit).
Whether method is used, it is important to minimize the impact of assembly and maintain bearing accuracy.
1. Pressing with a Hydraulic Press
When pressing the bearing using a manual press, etc., first calculate the press force required based on the interference fit between the shaft and inner ring (use a hydraulic press with a working pressure greater than the required pressure). Then, use the inner ring press tool to firmly press the inner ring into the shaft shoulder (do not apply force to the outer ring). After press-fitting, measure the accuracy of each bearing component to confirm proper seating on the shaft. Additionally, when assembling multi-row bearings, measure runout after assembly to correct for axial misalignment between the outer rings.
2. Shrink Fit
Take advantage of thermal expansion and contraction. Insert the bearing after thermal expansion. Generally, heat to 30°C. Importantly, when using resin materials for angular contact ball bearing retainers, avoid excessive heating; the maximum temperature should not exceed 80°C. Furthermore, as the inner ring contracts toward the shaft during cooling, play will occur between the bearing and the shaft shoulder. Therefore, after fitting, cool the bearing to room temperature and then press it down using a hydraulic press. Also, check for perpendicularity after cooling. When heating with a bearing heater, be careful to avoid excessive temperature rise. Use equipment equipped with a demagnetization device to remove residual magnetism.
Step 6: Secure the inner ring.
When installing and securing the bearing on the spindle, typically tighten the inner ring with a trapezoidal sleeve or precision bearing nut and bolt the front cover to the outer ring. When using a trapezoidal sleeve or precision bearing nut to secure the inner ring, keep in mind the following points.
1. Secure with a Trapezoidal Sleeve
A trapezoidal sleeve is a relatively easy securing method: inserting a sleeve, expanded by oil pressure, onto the shaft. After applying the required press-fitting force (tightening force), the oil pressure is removed. While securing the sleeve to the shaft, a tightening force is applied to the bearing.
However, since the sleeve secures the inner ring solely through interference fit with the shaft, it may loosen if the shaft bends or is subjected to moment loads.
For this reason, in most cases, the securing method shown below, combined with a bearing nut, is used.
2. Tightening with a Precision Bearing Nut
When tightening a precision bearing nut (precision lock nut), apply the appropriate tightening force according to the tightening torque regulations for precision lock nuts.
In addition, when using a precision bearing nut to secure the bearing, thread play can cause the nut to tilt, requiring fine adjustment to ensure shaft rotation accuracy.
3. The Relationship Between Tightening Torque and Tightening Force for Precision Bearing Nuts
Since the threads of the precision bearing nut, the threads of the shaft, and the seat of the precision bearing nut are sliding surfaces, the relationship between torque and tightening force will vary depending on the friction coefficient during tightening, so sufficient running-in is required.
In addition, it is also important to calibrate (correct) the relationship between tightening torque and tightening force using force washers or other tools beforehand.
At this point, the bearing installation is essentially complete. However, during the installation process, problems such as washer deformation, excess clearance in the front cover press, and excessive or insufficient clearance may occur. In the next chapter, we will provide solutions to these installation issues to ensure that the installed bearings maintain optimal operating condition and provide long-term, trouble-free operation.
